some Recent Piihlications concerning Diatoms. 33 



are invariably only two plates, which are always disposed 

 very asymmetrically — that is to say, if the left plate is nearer 

 to the upper end of the frustule, the right one is nearer to the 

 lower end. This is a very characteristic and constant feature 

 of Gyrosigma tenuissimum. 



Pleurosigma nubecula, W. Sm. (p. 77, fig. S8). 



The left figure is too sigmoidal to belong to this species ; 

 it seems rather to represent a small individual of P. deU- 

 catulum, of which it has the endochrome. The right figure 

 might be P. nubecula but for the endochrome, which, according 

 to my observations, is of the same type as in P. Normanii 

 (Et. s. I'End. d. D. pi. iv. figs. 1-5). 



Scoliopleura latestriata, Grun. (p. 84) [its right name is 

 ScoUotropis latestriata (Breb,), CI.]. 

 In the var. amphora the two opposite plates are united by 

 a common pyrenoid. It is very likely to be the same in 

 the type species also. Karsten represents them as being 

 separated. 



Tropidoneis maxima, Greg., var. ? (p. 88). 



Kepresents two species; the second figure (from the left) 



900 



Tropi(Io7ieis vitrea, \V. Sm., with cell-contents 

 Ann. (f; Mag, N. Hist. Ser. 7. Vol x. 3 



